Bless you, so very sorry you are in so much pain, this disease is incessant.
I too have contemplated A&E at times. The only thing that puts me off is that I could be sat in the waiting room for hours before even being assessed, I would much rather be coping with my pain in the comfort of my own home and bed.
I guess if you do go, there are two possible outcomes:
You get treated with more pain medicine and sent home
You some how miraculously are seen my someone with knowledge and understanding of Endometriosis. He/she may be able to help/advise you and maybe get you admitted so more investigations can be done. However, if you are already in the care of Gynae, chances are, they can't do anything for you and just tell you to attend your next appointment.
There are other options though. Have you telephoned NHS direct/ 111. I have found them to be helpful in the past.
Or, you could phone your Dr.'s Surgery, and ask for a call back from your Doctor, where you can express to him (tears if necessary) the severity of your pain and then ask him if you should attend A&E. Therefore you can attend with his recommendation.
Sending you strength to get through this, how and why can we be left in such pain. If we were animals they would put us down. We deserve fair treatment.
Much love xxx